1. Field of Invention
This invention relates to a map display device which transforms the coordinates of map data, and displays a map by using the transformed coordinates.
2. Description of Related Art
There are various types of vehicle navigation systems providing a driver with guidance information along a vehicle travel route, such as a navigation system that searches for a route to a destination and provides audio/visual guidance of characteristic information on the map regarding the route to the destination, and a navigation system that displays a map centering the present position and provides information about the vicinity of the present position, etc. For example, regarding a vehicle navigation system having functions, such as route search and route guidance, there are proposed systems, for displaying a travel image on a 3-D screen in order for the driver to comprehend information on the travel direction at a glance, and for displaying a road map from a bird's-eye view method, which magnifies a road map of the vicinity of the present position of a vehicle. (e.g. Japanese Patent Publication No. 160853/96, No. 166249/96 and No. 127861/97).
Some of the previously proposed systems display a wide-area map by setting a window display area on part of the bird's-eye view and designating the displayed area by a frame in order to improve the defects of the bird's-eye view this makes it difficult for the driver to sense distances and the dimensions of the road map area. Some other systems display a plane map or a bird's-eye view close to a plane map at the top of the displayed area within the predetermined area in order for the driver to receive accurate road distance information.
The above mentioned bird's-eye view displays a wider area than a plane map does, however, this applies to only one direction (Y direction) which is in the forward direction of the present position. Furthermore, as only the vertical direction of the screen is compressed, the sense of distance is different between vertical direction and horizontal direction. The distortion produced in the vicinity of the present position causes the driver to lose the sense of distance during the movement of the vehicle because the ratio between the actual travel distance and the distance shown by the movement of the present position mark on the screen differs according to the direction.